1. Field of the Invention
The present invention relates to a polymer latex, more specifically, to an ultra-fine particulated polymer latex obtained from the emulsion polymerization of unsaturated monomers. The present invention also relates to various compositions containing as an essential component the above-mentioned ultra-fine particulated polymer latex obtained from the emulsion polymerization of unsaturated monomers.
The compositions according to the present invention include coating or paint compositions, adhesive compositions, surface coating compositions for metallic materials, magnetic recording media, binder compositions for molding inorganic sintered products, additive compositions for hydraulic inorganic materials, sealing compositions or materials, binder compositions for non-woven fabrics, fiber processing or working compositions, reinforcing compositions for optical transmitting glass fibers, reinforcing compositions for hydraulic inorganic molded articles or materials, compositions for forming electroconductive films, film coating compositions for coated paper, additive compositions for paper making, resin compositions for toner, and photosensitive compositions.
2. Description of the Related Art
It is known in the art to prepare a polymer latex by emulsion polymerization of unsaturated monomers in the presence of an emulsifier. However, the polymer latex obtained by this method has a large particle size, and the film formed therefrom has the drawbacks of inferior properties such as transparency, smoothness, water resistance or solvent resistance, compared with a film formed from an organic solvent type polymer.
To alleviate these drawbacks, methods have been proposed in which the film properties are improved by obtaining a polymer latex having ultrafine particles by use of a polymerization initiator in which a minute amount of a transition metal ion is added as the accelerator in a redox catalyst comprising persulfate and a reducing sulfoxy compound, and then forming an appropriate three-dimensional structure in the polymer latex (Japanese Unexamined Patent Publication (Kokai) No. 60-170604, No. 60-170605, "Surface" vol. 25, No. 2, 86, 1987).
However, in these methods, problems arise in that the influence of the minute amount added of the transition metal used as the polymerization accelerator causes the particle size of the polymer latex to greatly differ, such that even when ultra-fine particulation is possible, the dispersion of the surfactant employed after emulsion polymerization may be small, which greatly increases the viscosity of the polymer latex formed, and thus ammonia water, ammonium phosphate or the like must be added before polymerization or during polymerization.
Further, although the polymer latex obtained by this method is crosslinked within the particles and/or between the particles, due to the influence of the temperature at which a film is formed, the film forming property, transparency or mechanical strength of the film are decreased, and when the polymer latex is stored by stationary standing over a long term, the particles are mutually coalesced or agglomerated to form coarse particles, causing a considerable white turbidity. Further problems arise in that layer separation occurs, and the viscosity is greatly increased. Therefore, this is not an industrially advantageous method.
Also, a method has been proposed in which the water resistance, etc., of the film is improved by obtaining a polymer latex by use of a certain kind of a polyoxyalkylene (meth)acrylic diester (Japanese Patent Publication (Kokoku) No. 54-19905). However, in this method, an ultrafine particulation can not be effected and the polyoxyalkylene (meth)acrylic diester has an inferior solubility and emulsifying power, and further, the film properties such as water resistance, etc., can not be improved unless a large amount of the above diester is used, and moreover, the film becomes sticky, thus causing the problem of an overly strong tackiness.